1. Field of the Invention
The present invention relates to a method and apparatus for controlling a disk drive, and, more particularly, to a method and apparatus for controlling a track seek servo of a disk drive, which reduces noise and also shortens the time required to seek a track.
2. Description of the Related Art
Hard disk drives include a plurality of magnetic transducers that can write and read data by sensing and magnetizing the magnetic fields of rotating disks. The data are stored in a plurality of sectors located in an annular track. Track numbers are located across each of the surfaces of the disks. The numbers of vertically similar tracks are referred to as cylinders. Hence, each track can be defined by a cylinder number.
Transducers are typically combined within a slider incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm, which has a voice coil located adjacent to a magnetic assembly that defines a voice coil motor. Hard disk drives typically include a controller and a driving circuit that supplies current that excites the voice coil motor. An excited voice coil motor rotates the actuator arm and moves the transducers across the surface of the disks.
When data are written or read, a hard disk drive may execute a seek routine for moving transducers from one cylinder to another cylinder. During a seek routine, the voice coil motor is excited by current that moves the transducers on the disk surface to a new cylinder. A controller executes a servo routine for ensuring that the transducers are moved to the center of a track of the correct new cylinder.
It is desirable to minimize the time required to read or write data from or to a disk. Hence, in a seek routine executed by a hard disk drive, the transducers must be moved to a new cylinder within a period of time that is as small as possible. Also, the time required to stabilize an HGA must be minimized so that the transducers can quickly write or read data and can be accurately located adjacent to a new cylinder within a very short time.
Generally, transducers can be rapidly moved to a target track by performing a seek servo control using a square wave acceleration trajectory. However, because a square wave has high harmonic frequency components, the square wave causes a mechanical resonance of the HGA and excites the mechanical components or assemblies of the HGA with a high natural frequency. Residual vibration creates auditory noise and undesired vibration and requires a settling period of time to stabilize the HGA. Mechanical resonance produced by a square wave according to conventional techniques increases the time required to write or read data to or from a disk.
A conventional technique developed to solve this problem is a seek control method using a sine wave acceleration trajectory. The seek control method uses an acceleration equation, a velocity equation, and a position equation, as shown in Equations 1 to 3 below, wherein constants Ka, Ia, and Tsk denote an acceleration constant, a current amplitude, and a track seek time, respectively.
                              a          ⁡                      (            t            )                          =                              K            a                    ⁢                      I            a                    ⁢                      sin            ⁡                          (                                                                    2                    ⁢                                                                                  ⁢                    π                                                        T                    sk                                                  ⁢                t                            )                                                          (        1        )                                          v          ⁡                      (            t            )                          =                                                            K                a                            ⁢                              I                a                            ⁢                              T                sk                                                    2              ⁢                                                          ⁢              π                                ⁡                      [                          1              -                              cos                ⁡                                  (                                                                                    2                        ⁢                                                                                                  ⁢                        π                                                                    T                        sk                                                              ⁢                    t                                    )                                                      ]                                              (        2        )                                          x          ⁡                      (            t            )                          =                                                            K                a                            ⁢                              I                a                            ⁢                              T                sk                                                    2              ⁢                                                          ⁢              π                                ⁡                      [                          t              -                                                                    T                    sk                                                        2                    ⁢                                                                                  ⁢                    π                                                  ⁢                                  sin                  ⁡                                      (                                                                                            2                          ⁢                                                                                                          ⁢                          π                                                                          T                          sk                                                                    ⁢                      t                                        )                                                                        ]                                              (        3        )            
When a voice coil motor (VCM) actuator speeds up or slows down along a sine wave acceleration trajectory, acceleration, velocity, and position trajectories as shown in FIG. 4A are obtained, and a VCM voltage trajectory is created using the trajectories of FIG. 4A, as shown in FIG. 4B. The VCM voltage trajectory has an asymmetrical shape that is inclined in a positive direction because a counter-electromotive force voltage is generated in a coil of the VCM due to the rotation of the VCM actuator.
If the counter-electromotive force voltage is not generated, the shape of the VCM voltage trajectory matches that of the acceleration trajectory shown in FIG. 4A. However, as the positive counter-electromotive force voltage generated by the coil of the VCM due to the rotation of the actuator is added to the driving voltage applied to the VCM, the voltage at the VCM driving voltage input port increases by the amount of the counter-electromotive force voltage. Thus, the VCM driving voltage trajectory has an asymmetrical shape, with the minimum voltage increasing by the counter-electromotive force voltage, which is a positive value.
Because the VCM voltage trajectory is inclined in a positive direction, the seek control method using a sine wave acceleration trajectory increases track seek time by about 10% of the track seek time obtained when a square wave acceleration trajectory is used.